Method and apparatus for intensifying electronic images



Jam. M, mm

c. CHILOWSKY 2,495,697 METHOD AND APPARATUS FOR INTENSIFYING ELECTRONIC IMAGES Filed June 8, 1946 6 Sheets-Sheet 1 INVENTOR CONSTANT/N (knows/(y ATTORNEYS Jam! L W@ c. CHILOWSKY 9 5 METHOD AND APPARATUS FOR INTENSIFYING ELECTRONIC IMAGES Filed June 8, 1946 6 Sheets-Sheet 2 ai -f a IN V ENTOR o/v5 TANT/A/ @H/LOWSKY )ulu lnln llalula w ATTORNEYS c. CHILOW SKY 2,495,697 METHOD AND APPARATUS FOR INTENSIF'YING ELECTRONIC IMAGES Filed June 8, 1946 6 Sheets-Sheet 3 P I (3.16 I I Q17.

INVENTOR. ti'o/vs TA xv 70v 0H/LOWSK c. CHILOWSK 9 METHOD AND APPARATUS FOR INTENSIFYING ELECTRONIC IMAGES Filed June 8, 1946 6 Sheets-Sheet 4 ATTOR/VEVLS Jam 3L WU c. CHILOWSKY 2,495,697

METHOD AND APPARATUS FOR INTENSIFYING ELECTRONIC IMAGES Filed June 8, 1946 I 6 Sheets-Sheet 5 Ill Il/I/I/ Jam 3531, W5 c. CHILOWSKY 2,495,697

METHOD AND APPARATUS FOR INTENSIFYING v ELECTRONIC IMAGES 7 Filed June 8, 1946 6 Shee s-S eet 6 F a @541. P: 0.35.

INVENTOR Wen o 14/81? v 2 3% g w H a ATTORNEYS Patented Jan. 31 1950 Tie-o STATES PATENT -'GFFF;I-.CE

METHOD AND APPARA .IN G ELECTR '-'17 Claims. 1

This invention relatesto a-metho'd and. means for reinforcing the luminous efiects that can be produced by electrons. 'It concerns particularly the intensification and amplification of images produced by means of electrons derived from a photooathode, or in a scanning electronic beam of a television tube.

The invention refers to image projection through light valves controlledby electrons or electronic beams, for instance'light valves with suspension in liquid. Most particularly "it refers to reproductionand light projection of opacity images produced by electrons projected intoa sensitive crystalline salt layer of alkali halides and alkaline earth halides such as'for instance, sodium chloride and bromide, potassium chloride and bromide'or other salts or materials having similar properties.

When the light is projected-through a layer of sensible salt on which an opacity image is formed (either by electronsof the photocathode or those of the cathodic beam of a television tube), a serious difficulty arises from the fact that the number of'electronsper cm. necessary to produce in this salt an opacity image 'su'ificiently strong for light projection, is relatively high. Furthermore, even for strong television cathodic beams, the surface of the salt layer and of its image must remain relatively small (for instance a few 0111. and the image can have only a very limited number of points.

For the same reason, 'a simple layer of sensible salt cannot be used for production and projection of an opacity image obtainable, from a'weak electronic image (corresponding for instance to a weak lighting of the photocathode).

The present invention is directed to eliminating these difficulties. This result is obtained by a new method of electronic concentration and by introducing a new special device denominated in this description the black filter.

The black filter is .a screen of a completely opaque material, generally insulating, which is provided with a great number'of very small holes or orifices filled with crystalline sensitive salt. A part of the light projected on one'side of the black filter passes through these "orifices tothe other side of the filter.

By appropriate means described below the electrons projected on the surfaceof the black'filter (either from the ph'otocathode, 'or'by television cathodic beam) are concentrated or condensedon the extremely small grains "of sensitive saltdis- 'seminated in the'holes or orifices of the "black filter, the total crosssectionof these grains of salt TUS FORlN'I-ENSIEY- ONIC.

ConstantinC hilowsky, New York, N. Y. ApplicationJune 8, 1946, Serial No..675,'502

"black filter can be the filter.

' -vision*with a very weak light,

'filterand' the microfilm it contains, an image of great brightness, andof "linear dimensions of the obtained on the other side of The invention has two principal-objects: "One is the intensification "of images of low .:brightness, and in particular, the vision (or photograph) of images through the darkness of the night.

"blacki'filter is atthebasis of these two solutions which will be successively described below.

.To make it possible toachieve 'clear and'sh'arp or at night, the invisible,*or veryfeebly lighted image, with itssuc- 'cessionpf variations in 'time,'is projected, for instance by means of an appropriate lens, onto a 'semitransparent photocathode, placed in a vacuum tube, the photocathode being able toliberate electrons in a number proportionate, at each point, to' the incident luminous intensity.

The black'filter is: formed by an'electrically insulating plate or layer of'material thatis completely opaque. This plate or layer, deposited on "a transparent "anode, contains a multitude of pores, ducts, or orifices'of appropriate profile extending through it comprising very fine constric- 'tions suchthat thetotal cross-sectionalarea of the constrictions (located "in the middle plane'of the filter or preferably forming an outlet toward the anode) is .extremelysmall in relation to the totalsurfaceareaiof the filter. The filter is completely impregnated with a continuity'of sensitive salt crystals, which fill the ducts and form -generally on'the side turned toward the cathode, a quasi-continuous crystalline layer of large sur- 'face'area.

.The electronic image, emitted .by the photocathode, is projected on and into this continuous salt surface covering the filter, forming in this layer a'negativetopacity image (or colored center image). Because of the small number of theproj-ectedelectrons, these opacities are negligible, and this opacity image is absolutely imperceptible.

.points of the order of 200,000 could be Under the action of the electric field (applied as aforesaid), the electrons forming the invisible image penetrate through the salt, into the multitude of very small constrictions or ducts of the filter, and form in these constrictions, before disappearing into the anode, concentrations and very condensed gatherings of electrons and opacitycenters. In the totality of the said constrictions (or ducts) filled with salt, there are thus formed heavy opacities, perfectly perceptible, which are able, through strong absorption of light, to form intense and visible shadow contrasts.

Thus is formed, in and by the totality of these salt points, a small opacity image, faithfully reproducing, point by point, the initial electronic image. I

The totality of the salt constrictions (ducts) with their opacities continuously varying as a function of the variations of the images striking v the photocathode, will: be called as mentioned,

'the microfilm, for by juxtaposmg the constrictions of the salt there would be obtained an extremely small film; and the image of this microfilm will be called, as mentioned, the microimage (or also microfilm) Thus, if we assume, as an example, a photocathode and a black filter of 100 cm. surface area; the distance between the filter ducts to be 0.3 mm.; the constrictions of the ducts at 0.01 mm. diameter, (i. e., the ratio of the filter surface area to the totality of cross-sections of the constrictions to be approximately 1,000), we shall obtain a microfilm of a total surface area of 10 m'mfi, and a micro-image composed of approximately 100,000 points. (Section ratios up to 100,000, and microfilms of fractions of one mm. could be obtained in black filters of a special construction, hereinafter described, and a number of achieved.) The opacity micro-image thus obtained will have the apparent dimensions of the black film. This image can be made clearly visible, on the other side of the black film, by the projection of a strong light, a small (or a substantial) part of which will go through the filter by passing through the salt-filled constrictions or ducts. The brightness of this image can be greatly increased by means of a second black-filter system with much larger ducts, and this second system will at the same time transform the negative r image into a positive one.

(Whereas the first black filter has the object of intensifying the shadow contrasts of the image, so as to form a perceptible negative image.)

The micro-image can be projected onto a screen; or it is made visible by direct projection, for instance, onto a frosted glass applied on the black filter. Or else the projection of the microfilms will be made by ultraviolet light, with a layer of suitable fluorescent material behind the filter.

The invention provides that the intensification of the shadow contrasts through the black filter can be combined with a method by which the electrons emitted by the photocathode are multiplied in number by emission of secondary electrons.

The invention provides particularly for a special method, whereby they intensification of the electronic image is effected without distortion of the image, by interposing, between the photocathode and the anode, and parallel to them, a series of special screens for the emission of secondary electrons, maintained at progressively increasing potentials.

Such special image preservation screens are of very fine structure, composed mainly of grids of very fine wire, very close-meshed and covered with materials suited for secondary emission, for instance, beryllium, beryllium oxides and the like. Or else, in a similar manner, it is possible to use thin metal sheets or foil finely perforated. The screens should be as close to each other as possible.

,An important variation consists in a system in which the successive electron emission screens are incorporated in a fine tubular structure guiding the electronic image, during its amplification, through a multitude of fine separate channels assuring the fidelity of the image.

The electronic image, intensified by the secondary-emission screens, can also be projected onto a homogeneous salt layer and will produce in this layer an image with much greater shadow contrasts than would be produced by the initial electronic image as previously described. But it is particularly important to combine the two shadow-intensifications, by means of the black filter, and by means of secondary electrons, by

r projecting the electronic image with secondary emission onto the black-filter salt. Thus will be obtained a. shadow-intensification proportionate to the products of the two amplifications.

The invention provides for two different methods of producing the intensifiedim'age in the salt and for projecting light through these images. In one of them, the formation of the opacity image and the projection of light through this image are separated in time, in order to avoid the possibility that the projection light, which can also reach the cathode, might disturb the formation of the image. This method has an alternating character, being able to utilize a kind of alternating current.

In the other method, the photocathode is protected from the projection light by a very thin sheet, non-transparent to light, but letting the electrons pass through it. The procedure becomes continuous, as the projections of electrons onto the salt and the projection of light through the salt can be made continuous and coincident in time.

Another important variation provides that the black filter is heated and the electrons enter the salt ducts through the intermediary of small metal areas.

Provision is made that the method of intensification, by black filter, of the luminous effects of the electrons may be used not only in i the case of formation of an electronic image,

properly called, but also for any electronic current, Whether it forms an image or remains a simple electronic current. Thus it is provided that the black filter may be placed, facing the photocathode, in the bulb of a photoelectric cell,

and that the variations of the microfilm, formed in the salt, be projected, by means of a light, onto a second photoelectric cell, the current of which can thus be amplified.

As previously mentioned it is also provided to use amplification by means of the black filter not only in the case where the electronic image is originated by a photocathode, but also in the case where it is formed by the scanning of a cathodic beam, for instance, in a cathodic oscillograph; and more particularly for the case of a cathodic television tube.

In the case of cathodic osclllograph and television tube, the black filter may be set in the place of the fluorescent screen. The microof the cathodic beam filter, suitably suspended in access? a zplate :of 'frosted glass,

Ultra-violet light for .order to receive directlyapositive image thegrid modulation. of theelectronic beam must be negative which canbe effected'byknown means.

'In' the cases of cathodic tubes the diameter can be made preferably equal to, or ofthe order ofythe distance between the orifices (ducts) of the-black'filter, so that at vthe moment of passage of the beam over the area belonging to an orifice, all the electrons of the electronic beam shall finally be concentrated on the very small section of crystalline salt "filling the constriction. It is evident that by taking the section ratio of only 100 (for instance, diameter of the beam' to be approximately 0.2 mm., and the diameter of the constrictions approximately 0.02 mm.) it will be possible to very considerably reduce the power (current and voltage) of the cathodic tube utilized, because only the very small power necessary to produce the microimage will be needed. And at the same time it will be possible to project the microfilm directly onto a rather large-screen, by means of ordinary light projection apparatus, and with essentially greater image brightness.

The invention also provides that the black a television tube, may be heated, with its microfilm of crystalline salt, to a high temperature, (for instance several hundred degrees C.) and this simply bythe thermic radiation of the projection-light, because the black filter can actually absorb a great part of this radiation.

To make practical such heating-which would greatly accelerate the disappearance of the opacities and shorten the frame period-4t is pro- .vided to arrange the black filter in a. special manner, wherein the small crystalline salt columns or areas are more or less hermetically imprisoned by layers, or deposits, of amaterial which itself does not develop any vapour tension at ,these temperatures, such as silica or quartz, or possiblyeorundum; said deposits will prevent any distillation of the heated salt. (Under these conditions the microfilm may even be periodicallysubjected, after suitable overheating, to a recrystallization, and this recrystallization could eventually be efiected under the action of supersonic or sonic high frequencymechanical oscillations, with a view to increasing the fineness of the crystals.)

.During the projection of the microfilm, a combined application of heatand of super-sounds may take place, the heating being efiected by radiation or any other process.

The invention provides also that in cases when the black filter is maintained at high temperature, the electrons of the beam are projected directly not into the sensible salt, but on small thin transparent metallic areas mutually insulated from each other, and covering the black filter as a regular mosaic, each such small metallic areabeing incontact with the-salt of the corresponding constricted duct, the metallic area being much greater thanthe section of the ducts. In the condition of high temperature the ,elec- .tronic charges produced in such ,area by the given section of the iducts.

concentrating :optioa-lly the surface with a "transparent -meta-llic layer, light being "concentrated on the salt duct through case of .a, fluorescent, light not suitable --beam, -:penetrate .directlyi inrthe isaltithroughithe metallic contact, in the ing opacity centers.

formv ;of electrons form- The invention generally provides .extensive -means'fo1rincreasing ithefproportion,of projected light penetratingithrough :the black filter, at a F'or -this purpose a multiplicity of small ilig'ht condensing elements,

light on the constricted part 0f the ducts, are provided at the entry side of: the black-filter.

In filters maintained at ordinary-temperature these concentrating --=elements are formed 1' from crystalline salt, and both :light and electrons are concentratedi-n traversing these elements. But

in the special caseof heated "filter and-electron concentrationthrough small transparent metallic area,- the light concentrating elements can be made also, for instance, ofglass covered on-its the the glass element, and the electrons beingconcentrated in thesalt of the ducts Joy-traversing the metallic layer; covering'an'dsurrounding the glass element-thismetallic" layer being in direct contact with the salt of the ducts.

On the other side -of thefilter '(exit side) a transparent ml'ilticellular optical system'may" be provided, to concentrate thelight comin "from the ducts in thedirectionof the projection screen of larger jdimensiomtakingadvantage of the fact thatthe light after j'having-traversed the filter constitutes a multiplicity of small luminous points, or punctual sources, composing the microfilm. A much greater brightness of the screen image can thus be obtained, than in the screen giving :only difiuse for such concentration :and direction.

The invention contemplates also the use of electronic concentration produced by the black filter for. control of light valves and specially of television light valves of different other'kinds and particularly of light valves with a liquid containing .a suspension .of small discoidal. particles orientable byan electric field produced and controlled by an electronic televisionbeam. 'In these cases, for the sensible crystalline salt is substituted the liquidcontaining theabove suspension. This liquid, asbelow described, will fill,the small ducts or preferably will be usedin a continuous thin layer.

Practical embodiments of the invention :are shown in the. accompanying drawings, .in which Figs. ,1, ,2 and 4- represent detailsectionsthrough different,formsofblack.filters;

Fig. 3 illustrates diagrammatically a step in the production of .a .black filter;

.Eig. eArepresentsa section througha, form offilter in which thejfront .and .back surfaces are specially shaped;

Fig. ,5 represents -a section .throughanother form of filter-combined .withrarsensitive. screen;

.Figs. 6, 7 and 8 represent. longitudinal sections through cathodicapparatus'in whichblackfilters areincorponated;

.Fig. 9v representsiassection througha light projecting ,disc;

.Figs. .10 and .11 represent sections through secondaryielectron. amplificationsystems Fig. 11A rcpresentsan enlarged .detailsection of part ofdlig. 11;

Fig. l2 represents .an senlarged ,end .,elevation of a modified form ..ofelectron multiplier;

Fig. 13 represents a side elevation of the multiplier shown in Fig. 12;

Figs. 14 and 15 represent sections through twin or tandem arrangements of cathodic apparatus;

Fig. 16 represents a section through an apparatus in which the electronic projection is curved;

Figs. 1'7 and 18 represent sections through image intensifying systems;

Fig. 19 represents, in section, a television tube having a black filter suspended therein;

Fig. 20 represents, on an enlarged scale, a section through the filter of Fig. 19;

Fig. 21 represents, on a greatly enlarged scale, a section through a modified form of filter;

Fig. 22 represents a section through another modified form of a black filter;

Figs. 24 and 25 represent detail sections of particular forms of electron-concentrating ducts;

Fig. 26 represents a detail section of a modified form of filter in which a liquid with discoidal suspension is substituted for the crystalline salt layer;

Fig. 27 represents a section through a modified form of light valve element, utilizing a glass with linear conductivity-and a fluid with orientable suspension;

Fig. 28 represents a section through another form of light valve having the elements of Fig. 27-combined with a black filter;

Fig. 29 represents a section through a further modified form of black filter light valve;

Fig. 30 represents a median section through a photocathode image intensifying device;

Fig. 31 represents a median section through a modified form of photocathode image intensifying device;

Fig. 32 represents a median section through a device similar to that of Fig. 31 but with formation of a positive image from an intermediate negative image;

Fig. 33 represents a median section through a particular form of black filter heating device;

Fig. 34 represents a longitudinal section through a television image enlarging and inten- H sifying apparatus;

Fig. 35 represents a median section taken at a right angle to the plane of Fig. 34;

Fig. 36 represents a perspective view of a block of material with linear conductivity, and

Fig. 3'7 represents, in section, a modified detail of construction of the end of a television tube.

Referring to the drawings,

Fig. 1 shows a black filter composed of a material which is itself completely opaque, but contains a multitude of pores, channels or ducts, traversing the material generally perpendicular to its surfaces through which a small part of the light can pass from side to side.

This figure shows a transparent glass support I, a very thin metallic layer '2, transparent to light and serving as anode, the opaque material 3 of the filter, provided with the pores, channels, or narrowed ducts 4, filled with a continuity of sensitive crystalline salt; 5 is a thin crystalline layer of the same salt, and 5 is a very thin metallic layer, transparent to light and to electrons, which can serve as an intermediate cathode, supplying a desired difference of potential between it and the anode, to ensure rapid passage of the electrons through the salt. This layer is optional, and the electrons, striking the salt, can themselves create the necessary field.

This black filter is preferably made coarsegrained and with short channels, permitting a possible maximum of light to pass.

Fig. 2 shows, greatly enlarged, a black filter comprising a single layer of grains. It can be made, for instance, by placing, on a transparent support (for' instance, of quartz), a uniform (regular) layer, formed by juxtaposition of small black glass, or black enamel, spheres or balls, as shown in Fig. 3. By subjecting this layer to suitable pressure and heating it to a temperature close to that of softening, it is possible to reduce the interstices I to as small a size as desired, thus achieving the above cited ratios between the cross-sections. This operation can be efiected, while keeping control of (or checking) the light passing through the system, for instance by exerting pressure by means of transparent quartz plates. Present technique permits producing small calibrated glass balls up to 0.1 mm. diameter which is amply sufficient.

Fig. 4.- shows a black filter constituted by a layer or plate 3 of a completely opaque material, (for instance, glass or enamel) with small perforations 4 filled with crystalline salt, in contact with the transparent anode 2, and the salt layer 5.

In the blackfilter of Fig. 4 the electrons projected on the salt surface 5, are concentrated in channels 4, upon traversing the corresponding areas of the layer 5. A great part of the light projected on the surface 5 is lost and cannot traverse the channels.

In Fig. 4A the crystalline salt layer 5 is of much greater thickness in order to permit a better distribution in the salt of the electric field driving the electrons towards the small ducts 4.

At the same time the surface of the layer 5 is shaped in a form of a multiplicity of juxtaposed bulbs or lenses 8 of appropriate curvature, calculated so as to concentrate optically on the small ducts 4 a great part of the light falling in approximately normal direction on the filter. The distribution of these light concentrating bulbs is such that each of them concentrates the light on the corresponding duct; 2 is the transparent anode, in contact with the salt of the ducts 4.

In the filter of Fig. 5 the electron concentration takes place through the cones 8, traversed by the electrons. A great part of the light projected on the surface of the cones can be condensed optically, by the bulbs of the cones 8, on channels 4' and can go by these channels through the filter. In order to increase the concentration of light the surface of opaque material 3 forming the Walls of the cones can be covered, by known methods, (before depositing the crystalline salt layer) with a discontinuous, electrically nonconducting mosaic of very small light-reflecting metallic grains.

In Figs. 4A and 5I is a support of transparent material (for instance glass or quartz) of a special form. The exterior surface of this support is shaped in a multitude of juxtaposed hemispheres, directing the divergent light, coming from the small points of channels 4', in nearly parallelly directed beams, which can be projected with much less loss on a screen. The plate I, which can be called light rectifier, permits also as shown in Fig. 5 to project the image without disturbance for instance on a photographic plate, or film, or moving film 9, through a relatively thick glass wall II] of the vacuum camera of the device.

If desired, the light rectifying plate I can be made of the same salt, and the anodic layer 2 could be placed on the bulb-shaped surface of plate I.

The surfaces of the cones B of Fig. 5 (and also 9 the bulbs 8' in Fig. 4A) may be covered with a thin metallic layer transparent to light and forming an intermediary cathode.

Taking into consideration that in medium fineness filters the distances between the small ducts can be of the order of 0.2 to 0.3 mm., and in coarse filters of large size, this distance may reach or exceed 0.5 mm, it is possible to form in the surface of the salt filling the cones, (or the surface of the thick salt layer in Fig. 4A) by means of appropriate mandrels, a multitude of juxtaposed and conveniently shaped small cavitations.

Or the filter channels, for instance these shown in Fig. 4, can be fashioned, starting with large channels or openings in the black enamel or black glass layer, and these channels can be progressively narrowed, under appropriate optical control, by pressure at a temperature close to that of softening of the layers material. These relatively large initial openings can also, if necessary, be made by a photoengraving process (for instance the potassium bichromate process), etching out the tiny bare (uncovered) areas with hydrofluoric acid, etc. The small openings can also be made in this manner.

The black filter can also be made of metal, the surface of which, including channels, is protected by a thin, non-transparent insulation layer.

The complete black filter composed from the opaque material 3, the channels 4 filled with salt and, if desired, the layer 5, will be shown as a single elem nt 113, wherever necessary in subsequent figures.

Fig. 6 shows diagrammatically in sectional view the reproduction and projection of an image with the aid of a photocathode and a screen of a sensitive salt, in the case of an alternating procedure.

In this figure, ll denotes a glass capsule with a very high vacuum; I 2 is a semitransparent photocathode, composed, for instance, of a thin layer of caesium and silver, suitably oxidised and deposited on glass; 2 is a very thin metal layer (for instance, of silver) transparent to light, deposited on glass and generally forming an anode; i3 is the black filter; Ill is a lens or objective through which an image to be amplified, for instance, a viewed object, is projected on the photocathode l2; for projection, for instance, in the form of a tube with a rarified gas under an electric discharge. The light of this tube is disposed, for instance, circularly around the objective and projected by a circular reflector it on the black filter through the semitransparent layer 2 constituting the photocathode.

55 is another circular source of light, and [B its corresponding reflector, injecting the light in the space between the photocathode and the black filter. This light is partially reflected from the photocathode on the black filter. These two sources may be lighted simultaneously or either one can be suppressed.

The operation consists at least of two phases, I and II, alternately succeeding each other.

In phase I, a high difference of electric potential is applied between the conductive layer l2 forming a cathode, and the conductive layer 2' forming an anode. During this phase, the exterior image to be amplified is projected by the objective i l on and through the photocathode, forming a so called electronic image at each point of which the number of electrons is proportional to the intensity of the incident light. Under is a circular source of light ultaneously with the action of a high electric potential applied between !2 and 2', these electrons are projected on and into the sensitive salt of the black filter l3 and traverse the salt for final disappearance in the anode 2'.

After a time suflicient for the formation in the black filter of a negative image of opacities, begins phase II: the difference of potential between 2' and I2 is suppressed and, as a result, the centers of opacity forming the negative image in the salt are immobilized approximately in their positions and distribution. The image formed on I 3 remains immovable during a few moments. Simultaneously with the suppression of the potential, the light of projection is lighted at I5. This light, passing through the photosensible layer l2, causes emission of numerous electrons. In the absence of an electric field, however, these electrons will not be projected on the crystalline layer, and will not penetrate the same so that they will not change the distribution of the electrons and will not modify the image.

Preferably, and in order to create a continuous visual impression the complete period of the alternating procedure may be equal to sec.

In the reestablishment of the phase I (after the immobilized during phase II, is imparted an apparent movement and with their old distribution, reaching the anode 2, and new electrons The negative and reversed image on the black filter l3, illuminated or projected by the light at l5, can be, if desired, reversed and rendered positive by any known method.

It is particularly provided to transform this negative image into a positive image, and to straighten it out, by projecting the image at l3 through the lens M on a second transparent photocathode E2, in front of which is a second black filter i3 in contact with the anode 2" within a container II with high vacuum similar to the container H. The image of opacity thus formed in the black filter I3 will be positive and straight and can be directly observed, or projected on a screen either by the light l5 and refiector it or by any other source of light and system of projection.

It is also provided that the projection light can be projected on the second black filter simlight from E5 by a circular source l5", the reflector I6 injecting this light in the space between photocathode l2 and the black filter. Either one of these sources may be sulficient.

It is also provided that the described system may operate with three phases, periodically alternating as follows:

Phase I'.-Potential applied between [2 and 2' (I2 serves as cathode); light I5 is out; I5 also out; potential between 52' and 2" either indifferent or zero.

Phase II.-Potential between l2 and 2 reversed (42 will be an anode); i5-illuminated, I5 is out; potential between l2 and 2" applied (I2' is a cathode).

Phase III'.Potential between I2 and 2' is inverted (i2 is now the anode) I5 is extinguished, i5 lighted; potential between l2 and 2" is inveted (i2 is an anode).

The operation of the three phases has an advantage in that, while l2 and 2" are strongly illuminated by the light l5, a portion of this light which could be reflected and reach the rear of the photosensitive layer l2, could not activate the crystalline layer l3, the potential between i2 and 2 being during these periods (phase III) reversed.

The coordination in time between the application of potentials and the illumination of the respective light sources can be easily assured by known means.

Fig. '7 shows a modification in which the systerns of projection of light by the tubes l5 and IS (with their respective reflectors l6 and it) are replaced respectively by the luminous sources l1 and I1, lenses I8 and i8, and mirrors (semitransparent) l9 and iii.

In Fig. 7 it can be seen that the positive image produced in the black filter of H is projected by the projection system l1, l8 and !9 through lenses on the large screen 2i.

If the original image was in infra-red light, then not only a visible image will be obtained, but also with greatly increased brightness.

In a modification of the black filter, called with a capacity curren a fine layer of insulation is introduced between the exit of the channel and the anode. This layer can be, for instance, of glass or of a very thin mica, of the order, for instance, of .01 mm. in thickness. The electrons become accumulated. under action of the electric field in the salt of the straight channels, and especially on the face of the anode, not being able to come from the channel toward the anode. In

this case, after the projection of the microfilm is achieved, the evacuation of the electrons from the salt is produced by applying a strong inverted potential which will drive the electrons, concentrated in the narrow channels, toward the large surface of the salt. To make possible their emergence from the salt, the latter is covered by separate grains or mosaic of photosensible elements such as caesium, which loses an abundance of electrons under action of the strong projection light.

Fig. 8 shows a modification or the process, in which the projection of light on the black filter, after formation of the image of opacities, is eifected by a special fiat disc 22, for instance, of glass containing light difiusing particles and strongly illuminated on all its parts by a light projected in it through its periphery (according to known methods); in this figure, 23 is a glass chamber with high vacuum; It is an objective, projecting the image on the photocathode l2 deposited on the disc 22. The disc 22 is rendered luminous by the peripheral illumination, according to known methods, by the light of the circular tube 24. The light enters this disc through its peripheral thickness 23 A second similar disc 22' lighted by the source 24, supports, at one side the black filter l3, and the other side the second photocathode l2. I3 is the second black filter, supported by a separate plate, or by a wall 23' of the chamber. The operation is the same as was explained for Fig. 6.

Fig. 9 shows a variation of a light projecting disc comprising a fiat capacity 22 filled with rarefied gas and limited by the walls 22. The gas disc 22 is strongly illuminated by electric discharges introduced by two separate electrodes 22.

As previously stated, it is provided, in order to increase the sensitiveness of the system, to multiply, by means of secondary electrons, the numher of the electrons projected onto the black filter, as compared to the electrons originally emitted by the photocathode. Such a multiplication can be obtained by placing correspondin amplification devices between the photocathode and the black filter (for instance in Fig. 8), and by sending a peripheric light projection into the space between electron multiplying device and the black filter.

But the most important results can be obtained by combining the multiplying device with the continuous method of image intensification.

Figs. 10, 11, and 12 show the image amplification system by secondary electrons.

Fig. 10 shows schematically an arrangement for intensifying the electronic image by a multiplication of the secondary electrons, by means of very fine mesh grids, inserted between the photocathode I2 and the transparent anode of the black filter l3.

In this figure, Eff-25 are fine metallic grids, for instance of metal wire, covered with a material (such as beryllium oxide or the like) that is able to emit secondary electrons. Said grids are set, for instance, in a supporting ring 26 of insulation, and are insulated in regard to each other. A progressively increasing difference of voltage, schematically indicated by batteries 2l-27l is applied between these grids by means of electrodes 23-28 An appropriate difference ofpotential is also applied between the photocathode l2 and the grid 25, as well as between grid 25" and the anode of the filter IS. The direction of the electric field between the photocathode and anode is the same through all the grids. H" is the wall of the hermetic glass case, inside which a high vacuum prevails, and it is the lens which concentrates the image on the photocathode [2. The light can be projected by one of the previously described means.

In order to avoid deformation of the image, the distance between the grids EE -25 is preferably made as short as is possible and compatible with the applied difference of potential. The distances between the grids and the cathode, as well as the anode, are likewise made small.

Fig. 11 shows a secondary electron producing device composed of a succession of finely per-- forated sheets with secondary emission material deposited on the surface of the perforations, and of similarly perforated sheets or laminae of insulating material inserted between the first named sheets, forming together channels guiding the electrons. In this figure 29?.9 are the perforated sheets with secondary emission material; 3ii-3il are similarly perforated insulating laminae; 3! are channels guiding the electrons. The interior surface of each channel is thus composed of an alternating succession of rings of secondary emission material and of insulating material.

In an important variation shown in Fig. 12 the channels are constituted by mutual application of thin undulated laminae 32, 32 52 etc. of

' insulating material, preferably of glass, the channels being parallel to, and formed by the undulations. Fig. 13 shows the surface of such an undulated lamina, for instance 32 oriented to 32 33 are the lines of contact between the undulations 32 and 32 and narrow bands of secondary emission material 34 are deposited on the surface of the laminae on both sides, with appropriate distances between the bands. The thin undulated laminae are preferably of very thin glass, the thickness of which can be of the order,

for instance, of 0.01 mm; the dimension of the undulations and of the channels can be of the order, for instance of 0.1-0.2 mm. in diameter, and can thus intensify electronic images of very fine structure with a very great number of points. The bands 34 deposited on different undulated laminae at the same distance from front and back edges are in mutual contact when the laminae are assembled and are at the same potential.

Fig. 14 represents the case in which the formation of the opacity image and the projection of light through this image are not separated in time, but are continuous and synchronous. This is generally achieved by placing a nontransparent screen between the photocathode and the black filter. This screen permits the electrons, having suflicient speed, to pass through. In this case the light does not pass through the photocathode but is projected from the periphery into the space between the nontransparent screen and the black filter and penetrates more or less obliquely into crystalline layer. Consequently, at no time can any part of said light fall on the photocathode and disturb the electronic image produced by same.

The screen preferably consists of an extremely thin glass lamina on which a thin layer of metallic lithium is deposited (for instance, by vaporization in vacuum), the thickness or this layer being just suincient to assure its non-transparency for light.

In order to avoid or reduce the possible fluoresence of the metallic layer under the action of incident electrons, the difference of electric potential applied between the photocathode and the protecting screen will be reduced approximately to the value strictly necessary to assure the penetration of the electrons through the screen while losing the greater part of their kinetic energy. (In contrast to the case of a fluorescent screen, where great electron velocities are needed, the penetration of electrons into the crystalline salt layer requires only small velocities.)

For the same purpose of avoiding the fluorescence of the protecting electron producing devices are installed between the photocathode and the black filter, the protecting screen will preferably be inserted between the photocathode and the secondary electron producing device (for instance, at the entry or" this device). Thus the danger of fluorescent trouble will be limited to the action of only primary electrons in relatively low number.

Fig. 14 shows schematically, in cross section, a double (twin) arrangement, with two compartments, dark and light.

In this figure l |l l are the glass walls of the holder containing 4 compartments; 35 is a dark compartment one end of which is formed by the photocathode i2 deposited on the transparent wall II, and the other end by the nontransparent screen 36 with its support; the lateral walls H and H are or" black non-transparent glass. 37' is the strongly lit compartment its ends formed by the non-transparent screen 35' and by the black filter l3. 2 is the transparent anode deposited on the very thin plate 38'.of mica, or transparent or frosted glass, 39 is a circular peripheral source of intense light; 40' is a reflector.

Juxtaposed to this two-compartment arrangement is a second similar system with two compartments, 35 (dark compartment) and 31 (light compartment), said system, as explained,

screen when secondary transforming the negative image into a positive image. In case a second black filter is used, this second system produces a second luminous intensification of the image. This second system comprises the same thin glass sheet 38, the right side of which is covered by the semitransparent cathode I2 the non-transparent screen 36 the black filter I3 the anode 2 the anode support 38 (the anode may, if desired, be set directly on the wall H 39 is a source of light, similar to 29', lighting the compartment 31 40 is a reflector. The thin transparent plate 38 supporting the transparent anode and the black filter I3 can be of glass the exterior surface of which is shaped as shown at l' in Fig. 5, with a multitude of hemispheres.

Fig. 15 represents schematically a variation of Fig. 14, wherein 4i and M are already described (for instance, Fig. 13) arrangement for amplification of the electronic image by secondary electrons. The non-transparent screen 36 and 36 can be supported by the last grid of the devices 4| and M The light injectors 39', 39 are exterior to the glass holder H, the light penetrating through the transparent parts 42'. 42

The screens 36, 36 can be also composed of a very thin lamina or layer, for instance of alum inum, of a thickness of the order of 0.5 micron. But, as previously mentioned, it is particularly provided to make this'layer of lithium or its alloys, of very low density, which will be more permeable to the electrons. The metallic screens 36' and 36 will preferably be covered on their side facing the light compartment, with a Very thin layer of glass or quartz, so as to avoid the liberation of photoelectrons by the action of the strong light; or this glass layer or lamina may form a very thin support for the non-transparent metallic deposit, forming the screen.

In order to simplify the projection of light through the crystalline layer and the black filter, provision is made for projecting the electronic image onto the crystalline layer and the black filter along curved trajectories produced, in accordance with known methods, by the action of an appropriate magnetic field on the electrons forming the image. The photocathode and the crystalline layer may form an angle between them, for instance of with the strong light being, in this case, projected vertically onto the crystalline layer of the black filter. Fig. 16 shows schematically an example of such an arrangement. In this figure, i2 'is a semitransparent photocathode, set inside the bulb d3; M, 5 are two permanent magnets in the form of rings, which cause the deviation of the electronic image; [3 is the black filter, whereon the electronic image is projected. Arrows 46 indicate the beam of light projected onto the crystalline layer and the black filter. Bulb 43 is transparent in back of the photocathode I2, as well as in its upper part 43' and its lower part #3 in order to let pass the light beam M5, on the black filter l3. Tubular shields 31, 47 47 may be provided to prevent light .5 from reaching directly or by reflection, the photocath-ode 52; in addition, a screen 35, non-transparent to light, but letting pass the electrons, can protect the photocathode against the light. This screen should be kept at an appropriate potential between that of the photocathode and that of the anode.

In general the secondary emitting devices may be combined either with the black filter, as described hereinabove, or with a fluorescent screen.

Indeed, making use of the fact that the apparatus shown in Figs. 12 and 13, with secondary electrons, permits, because of its particular very fine structure, not only to intensify the electronic flux, but also to greatly intensify the electronic image as such, without deforming it, provision is made to project said intensified electronic image onto a fluorescent screen, sensible to electrons, and to obtain in this manner a visible intensified image.

Provision is also made to subsequently project this image of the fiuorescent screen onto the photocathode of the above described system in order to efiect further intensification of said image by means of the black filter system. This case is shown schematically in Fig. 17.

In this figure, the electronic image of the photocathode I2 is intensified by the secondary emission system 4 l and is projected on the fluorescent screen 69, the electrons first passing through a thin non-transparent metallic layer 48. The thin metallic layer 48, indicated by a zigzag line, constitutes at the same time both the anode and the screen protecting the photocathode l2 from the light of the fluorescent screen Q9. The fluorescent light traversing the very thin plate 38 of glass or of mica, strikes the semitransparent photocathode I2 which produces a strongly intensified electronic image. This device 4! is projected on the black filter It. The nontransparent screen 36 protects the photocathode l2 from the projection light of the peripheral source 39.

Fig. 18 shows a double intensification with two successive fluorescent screens, in which the black filter is replaced by the fluorescent screen 49', having as explained a light protecting layer 48.

The double intensification systems shown in Figs. 14, 15, 1'7 and 18 have the advantage that the high potential differences between the photo cathode and the anode (and the corresponding grids) can be applied in parallel, as shown on Fig. 14. In general and depending on the particular case, it is possible to combine difierent and various manners of intensification of the electronic image by the black filter (with or without amplification by secondary electrons) with its intensification by means of projection onto a fluorescent screen.

The invention also makes provision for a method to accelerate the disappearance of the opacity images (as well as to intensify said ages) b the application to the sensitive crystal" line salt layer of high, and very high, frequency elastic oscillations, in accordance with applicants copending application, Serial No. 599,572, filed June 15, 1945.

This can be obtained, for instance, by using a plate of piezoelectric quartz with strong high frequency resonance oscillations as the support of the black filter.

The above described invention may have many different practical applications, including some that are listed as follows:

A. Direct clear vision, or direct clear projection onto a screen, at night or with very poor light (using either the remaining light of the sky or the stars, or else natural infra-red light).

Particularly, clear vision at night of the road, its surroundings, landscape, etc. during trips by car, boat, railroad, airplane, etc.

B. Taking of pictures, ordinary or cinematographic, or television, from an airplane at night.

Cameras or apparatus for night vision, of large linear dimensions, with large plastic lens and with '16 black filters of large linear dimensions (for instance of several decimeters or more) could be produced relatively easily. They may form windows for clear vision of landscapes when traveling at night, for instance by boat. Or else they may project such nocturnal vision on large clear window-openings facing the obscurity of night (on boats, airplanes, etc.).

C. In general, suppressing the obscurity of night for mans vision, achieved not by external lighting, but by an artificial intensification of mans power of vision.

D. Ordinary photography, rapid or instantaneous, with poor light or at night.

E. Taking cinematographic pictures at greatly reduced lighting, or even at night, without light.

F. Taking television pictures in same condition of reduced lighting or at night.

G. Eventually astronomic photography with greatly reduced exposure.

When utilizing the black filter in cathodic oscillographs and in television tubes, a single black filter is generally used, preferably with a relatively moderate ratio of sections (for instance of the order of 100) Preferably the filter will be heated in order to accelerate the disappearance of the images, and the invention makes provision for special black filters that will be adapted to be maintained at a high temperature, which may reach or surpass 500 C. Other means of acceleration, such as ultra-sonics or infra-red rays, may be used instead of, or in addition to, the high temperatures.

Figure 19 shows such a black filter suspended in a television tube and heated for instance by the radiation of the source of projection.

In this figure, 5B is the television tube; 5! its cathodic scanning beam; i3 is the black filter, suitably suspended in the vacuum by the supports 52, so as to reduce to a minimum heat losses due to conductivity; arrows 5% denote the projection light, projected onto the filter (in the majority of cases, on the side of the cathodic beam). The intensity of the radiation of the source, principally the infra-red radiation, ab sorbed by the black filter, is sufficient to compensate the thermic losses of the filter, due to the radiation in the vacuum, for instance up to 500 C. The temperature of the black filter may be regulated, by regulating the absorption of the infra-red radiation of the source by suitable screens, or by a screen with water circulation interposed between the source and the television tube. The filter may be automatically maintained at a constant temperature, by known means, through an automatic variation of the thickness of the absorption-layer as a function of the radiation of the black filter. The electric assembly diagram of such a tube is known.

Fig. 20 shows, greatly magnified, a part of the black filter, similar to the one shown on Fig. 5; the convex surfaces of the salt cones are covered by a very thin transparent quartz or silica layer or film 54, its thickness being of the order for instance of micron, or fraction of a micron, said layer or film letting pass through it the electrons projected onto it. A continuous metallic layer 55, also extremely thin and transparent both to electrons and to light, may optionally be interposed between the salt and the quartz layer, in order to form an intermediate cathode. The quartz and the metal layers are deposited preferably by vaporization in vacuum. Preferably, the quartz layer is deposited so as to adhere, around the conical passages 3' to the opaque material of the filter. Due to the protective crystalline salt 3 even layer 54, the when heated to a temperature of 500 C., and above, cannot undergo any vaporization or distillation in the vacuum. The thickness of the salt layer remains constant, as does also its shape. An even greater advantage is the fact that high vacuum may be maintained in the television tube even at the highest temperatures of the salt. (A thin layer of metal, transparent to light, could contribute very little to this tight condition). The support I of the filter should also be of quartz or of glass covered with quartz, and can be shaped as in Fig. 5. Other forms of black filter could also be hermetically protected in this way. The arrows 53' show the path of the light.

It is known that if crystalline salt and a metallic electrode, which is in direct contact with it, are maintained at a high temperature, for instance, of the order of several hundred degrees (2., the electrons can, under the action of a suit able electric field, pass directly from the metalli electrode into the salt and form in that salt opacity centers.

The invention makes use of this fact to make provision for an important variation of the black filter maintained at high temperature, wherein the electrons. instead of being projected directly into the salt, are projected onto the metallic electrodes and then enter the salt through the intermediary of said electrodes. This method is called method with intermediary electrodes and such a filter is shown in Fig. 21. In this figure, 3" is a thin sheet or layer of insulating opaque material, containing a multitude of orifices, perforations, or narrowing ducts 4" filled with crystalline salt; 2 is the anode; l is a support made of glass or quartz. The surface of the filter (including the surface area of the ducts 4") scanned by the cathodic beam is covered by a thin metallic layer. But this layer is a discontinuous one and is composed of as many thin metallic pieces 56, electrically insulated from each other, as there are ducts or passages 4" in the filter.

The said metallic pieces, or areas, have linear dimensions much larger than those of the ducts or passages, and each such metallic piece is in direct contact with the salt of the corresponding duct which the said metallic piece covers. These small metallic areas, cover almost the WhOle of the filter (except for the very fine separation lines 57, which are bare of metal), and the ratio between the totality of the surfaces of the metallic pieces and that of the minimal-sections of the ducts may be the same as the aforecited ratios between the filter surface and that of the ducts The filter will preferably be covered with the thin protective layer 54' of quartz, allowing to pass electrons and light. Said protective layer 54 should be continuous and will preferably adhere to the opaque material 3" of the filter, along the lines 51, thus insulatin the metal pieces one from another. The cathodic beam 5! will preferably have a cross-section approximating the surface area of one of said metal pieces. The thick ness of the metal deposit of said small areas 56, above the salt of the ducts 4" and in contact with the salt, is sulficiently small to allow light to pass. On other parts of the filter the thickness may, if necessary, be greater.

The electrons of beam 5| enter the metallic area 56 which is in contact With the beam, pass through the metal in the form of an electric current, to the point of contact with the salt, and enter heavily condensed into the salt, under the action of the temperature, and of the electric field. This field is created by the presence of the electrons of the beam between the metallic areas and the anode. "Fig. 22 shows'a plan-view of the filter of Fig. 21, with the covering layer 54' removed or absent. 4" are the small squares of metallic deposits; and Slarethe lines of separation and insulation between the metallic area-pieces. These lines may be produced by a fine tool or by means of a photogravure, as suggested."

The opacities thus produced by the scanning beam in the salt of the black filter, reproduce faithfully, in the microfilm of the salt, the television image. All electrons of the electronic beam, falling on a metal area piece, are immediately concentrated on the corresponding point of the microfilm of salt. This method ofconcentration of electrons in the grains of salt by means of intermediate electrodes has, in relation to the previously described method, the great advantage that the electrons, inorder to concentrate in the final ducts, need not pass through the above described cones or layers of the salt, but penetrate directly, already concentrated, into the tiny part of the salt which is really useful, where the microimage' is formed and the microfilm, properly called, takes form. Thus one gets rid of the cumbersome andunnecessary parts of the salt. This method also eliminates the parasitic time of the passage of the electrons through the cones and concentration zones, leading to the narrowed ducts, and the parasitic high voltages necessary for these passages. These voltages may here be used to intensify the useful field in the ducts. At the same time the filter construction is simplified and it is possible to use filters and salt layers of much smaller thickness.

The black filter of Figs. 21 and 22 gives passage only to a smallpart of the projected light. But in an important'modification light concentrating elements (such as lenses, spheres or cones) covered with a very thin metallic layer transparent for light are incorporated in the black filter. These elements, on one hand, concentrate optically the projected light on the small grains of sensible salt constituting the microfilm of the black filter; and, on the other hand, concentrate the projected electrons on the same grains of salt by conducing them into these grains by metallic conductivity of the respective transparent layers covering the concentrating elements.

An example of such a black filter is shown in Fig. 23, in cross-section through a few elements.

In this figure, l is a light rectifying transparent support of the black filter; 3, the opaque material of the black filter shaped in the form of a multitude of concavities 58; 4" are small orifices, filled with salt, in the bottom of these concavities; 59, transparent spheres, for instance of glass, fixed in the concavities 58; 60, a transparent metallic layer deposited on the spheres; 5| are lines indicating the scanning beam of the television tube; 53'. the arrows indicating the light projected on the black filter.

One of the possible modes for construction of this filter is the. following:

.The black body 3' of the filter is shaped from glass or enamel plate by a mandrel complementary to that used for shaping the glass platel. The known technique can realize calibrated glass spheres to a diameter of 0.1 mm. After having applied the layer '60 tolthespheres and having introduced and fixed the spheres into the concavities, the crystalline salt layer is deposited, by distillation, on the side oriented to the anode. The salt penetrates through the orifices' l until the metallic layers 60, and assures electric contact with the spheres 59.

The excess of salt deposit on the surface of 3 can be taken away, but that is not obligatory. After that, the anodic layer 2 is deposited on the surface of 3', including the salt in 4", or on the crystalline salt layer if it is not taken away. The glass body I is then applied, or sealed, to the anodic layer 2. A solid transparent plate 6i can support the whole. Naturally the metallic layers of the spheres remain electrically isolated from each other. a

In this black filter a relatively great part of the projected light can go through the filter, and can conserve approximately its direction after passing the filter. It is important to note that, as a result of such optical concentration of light on the small grains of salt, these grains, if desired, can be strongly heated and maintained at a higher temperature than' the rest of the filter. This heating can be regulated by controlling the admission of thermic infra-red radiation. Also such concentration can make more effective the possible extinction of images by infra-red radiation. By appropriate modification of the technique it is possible to use salt spheres instead of glass spheres.

Fig. 24 shows a variation in which the light concentrating bodies are not spheres but cones, coated on their surface with thin transparent metallic layers 60. These cones can be of glass, quartz, or of the same crystalline salt,

In Fig. 24 is shown that a continuous crystalline layer 62 of salt can be used, this layer being in contact with the transparent but metallized ends of the cones 63.

This form has the advantage that the strong concentration of electric charges on the needleshaped ends of the cones can assure the transfer of electrons from the metal into the salt at much lower temperature, and even at ordinary temperature if a sufficiently high voltage is used.

The invention provides also that in the above described cases through intermediary electrodes? the high voltage current of the electronic beam can be used to heat the salt grains and to maintain them at much higher temperature than the rest of the filter.

The index of refraction of the glass spheres or cones will be chosen so as to concentrate the greatest possible part of the light on the salt grains in contact with the spheres on the opposite sides or with the ends of the cones.

Empty reflexion cones or pyramids provided in the opaque material and metallized on the interior side can also be used for partial concentration and direction of light but with much lower efiiciency. i i

In cases of black filters with very fine orifices not realizable with other methods it is provided to make greater orifices and to then reduce their diameter to the desired fineness by progressive deposit (for instance by vaporization in vacuum) of insulating non-transparent material or composition. This method can also be used for the formation of crystalline salt grains, as shown in Fig. 25, where, a salt layer 64- is deposited onthe interior surface of the cone 65, this deposit of electronic concentration special and being completely same direction with a good transparency'in other forming on the end of the cone the crystalline grain 66'. A second deposit of the transparent metallic layer 66 forms the intermediary electrode receiving electrons and transmitting them to the salt grain 8 If desired a light concentrating body formed, for instance, by continua.- tion of the salt deposit can fill up the cone.

It is also possible to introduce the secondary electron producing devices in the cathode tele-. vision tube by placing them directly on the black filter.

Fig. 26 shows schematically the case in which the light controlling layer is constituted by a liquid containing a suspension of small particles of discoidal shape, which are oriented (according to a known method) by electric fields produced by the scanning electronic television beam. Fig. 26 differs from Fig. 24 in that a layer 61 of a liquid with discoidal suspension is substituted to the crystalline salt layer 62. In Fig. 26, the liquid layer til with its suspension is in direct contact, on one side, with the transparent anode 2, and, on the other side, with a thin lamina 68 of mica or glass, the ends of the cones 63 covered with the transparent metallic layer 56 bringing electric capacity charges which orient the suspension and increase the transparency of the liquid. But the thin layer 68 can be omitted, and the metallized ends of the cones 63 will be in this case in direct contact with the liquid; or the liquid may simply be substituted for the salt in the ducts 4 (for instance in Figs. 22 and 23) In the case using a'liquid with suspension the black filter does not need to be heated, although a slight heating may be favorable in reducing the viscosity.

Introducing the principle of the black filter for light control through a liquid suspension, present's, comparatively to the same system without black filter, the same great advantages. But a advantage is introduced by the fact that the rapidity of disappearance of the micro-image on this liquid microfilm can be easily controlled and increased at will by small displacements of the liquid in the form of a continuous or discontinuous current, or in the form of small periodical oscillations having, for instance, the frame frequency, which can be used for control of image disappearance, and of storage effects. The technique of liquid television valves is known and will not be described here.

The invention provides also an important modification in the construction and distribution of the black filter, applicable for both types of light valves: with sensible salt layer or with suspension liquid or otherwise. It is based on use of a new special kind of glass (or plastic) having in one direction-generally normal to the plate or sheet-a relatively great electric conductivity, transparent at least in this directions. Such glasses, and glass (or plastic) blocks and plates, can be made by incorporating in the glass mass or in the plate a multiplicity of extremely fine and straight conductive strands extending from one surface of the plate to another.

Such glass can be made, for instance, by preparing and fixing together at a conveniently high temperature a multitude of thin parallel glass laminae, the surface of each lamina having a deposit of a multitude of a very fine parallel or non-parallel lines of appropriate metal or other conductive material. After a careful welding of If: these laminae, or other mode of mutual fixation,

the glass block can be cut, perpendicularly, or at any desired angle to the metallic ducts, into plates of the desired thickness. The glassv itself and method of its fabrication-are covered by copending application Serial Number 682,992, filed July 12, 1946. For the purpose of the black filter the two surfaces of such a plate 61 with linear conductivity are covered, preferably on both sides, as shown in Fig. 27, with a multiplicity of small separate and mutually insulated transparent metallic areas 68 and 68,. each pair of opposite areas being mutually electricallyconnected by at least one very fine conductive strand T; the narrow lines or bands separating the small metallic deposits are covered with non-transparent insulating materialli (on one side) and 72 (on the other side) i3 is the liquid with orientable suspension, forming the light-valve and being in direct contact with the metallic areas 69; 2 is the transparent anode and M is the tran parent .plate supporting the anode. i

The electric charges of the electronic beam scanning the metallic areas 68 are immediately transmitted respectively to the connected areas 69, the electric field of these charges insuring the orientation of the suspension. The suspension liquid 73. having generally a certain although very small electric conductivity, the orientation disappears as soon as the potential in 69 has dropped sufficiently and that is a great advantage of this method (although the usual disorientation by second scanning with low velocity electrons can be used) The light valve screen represenated in Fig. 2'7 B is a new type of light valve with direct contact with the liquid.

In the arrangement of Fig. 27 a crystalline layer of sensible salt can be substituted for the liquid suspension layer l3, provided that the screen is maintained at high temperature.

The light valve of Fig. 27 uses no electronic concentration. But it can be transformed into a black filter light valve with electronic concentration, with light concentration, and with micro-image formation on a microfilm, as shown in Fig. 28, by depositing a layer of completely opaque insulating material on the surface of the plate 76 in contact with the active valve material. This non-transparent layer covers all the surface with exception of the small areas 11 which remain in direct contact with the active material. and through which pass the light concentrated by the convexities I8.

The transparent metallic areas form with the anode 2 an electric condenser periodically charged by the scanning beam. By making these areas 63' (under the black deposit) greater or smaller onecan change the duration of orientation of the suspension, or the rapidity of disappearance of the opacity image in the salt.

Fig. 29 shows a variation in which the active valve material (sensible salt or liquid suspension) is contained in the cavity 19. '(These cavities can be of light concentration, for instance, by a photogravure procedure.) The formation of these cavities will greatly facilitate the deposit of the active material and of the opaque layer. In cases when the cavity 79 is filled with sensitive crystalline salt, it is possible to insure the metallic contact with the salt only through the pointed end of the conductive strand l0. In these conditions of extremely concentratedelectric forces the electron' will b'eable to'go from the metallic point obtained and exactly positioned in the focus stitute the exterior 22.,,. into the salt even at ordinary temperature, or at a lower temperature than normally needed.

The black filter of the type of Figs. 28 or 29 can constitute the wall of a television tube, and the plate 61' of the filter can be soldered into the tube, the metallized convexities being ex-' posed to the scanning beam. The deposit of active material (salt or suspension liquid) will constructure which can be changed without opening the tube. Alternatively, the wall of the television tube exposed to the scanning beam may consist in the glass plate6'! with linear conductivity, shown in Fig. 27, of sulficient thickness and of completely tight construe tion, with the double mosaic of transparent metallic areas 68 and 69. The black filter, of the type for instance of Fig. 28 or 29, will be con veniently firmly applied to the glass wall with linear conductivity, and the projection light, and also the electric charges of the beam will be directly transmitted through this wall to the black filter, which becomes in this way completely exterior and interchangeable, and working at normal atmospheric pressure.

The black filter of Fig. 29, if used with liquid suspension, has the advantage that the suspension liquid contained in small closed capsules cannot undergo any objectionable settling. Furthermore, the exposure of such a black filter to mechanical oscillation, for instance of supersonic frequency, will insure the homogeneous distribution of the suspension in the liquid.

The invention provides also that high frequency mechanical oscillation may be used in order to accelerate the disorientation of previously oriented particles suspended in the liquid (in valves using such suspension). Normally, after the disappearance of electric forces orienting the sus pension in the direction of the field, the particles return to their normal chaotic orientation, obturating the light along a special time curve occupying an appreciable time interval independent from the previously applied electric field, On the contrary, under influence of mechanical oscillating in the direction normal to the surface and of a very high frequency, the particles become oriented parallel to the surface, that is, in a direction perpendicular to that produced by the electric field. It becomes thus possible, upon introducing by these oscillations, this active light extinguishing orientation on one hand and by in,- creasing the electric field on the other hand, to obtain an essential shortening of the lighter:- tinguishing time interval, and an essential shortening of the television frame period. A quartz plate of appropriate thickness, constituting, for instance, the support of the anode, and maintained in suiiiciently strong mechanical resonance oscillation by an appropriate high frequency oscilltating electric circuit, can produce this oscillaion.

The glass with linear conductivity cannot only form part of the black filter, or constitute the Wall of the television camera, bringing the scan hing phenomena to the other side of the wall, but this glass permits very important developments and improvements of the described method of image-and specially television imageintensification and projection. f

Indeed, the described light valve control with sensible salt or liquid suspension can generally be operated by electric charges and potentials produced by projected electrons. The invention provides that this variation of electric charges and potentials can be transmitted-by means of this access? glass or plastic with linear conductivity from the vision camera or from the television tube at an appreciable distance, and at this distance can exert its action on the described light valve screen or black filter. Moreover, it is provided that by convenient shaping and cutting and adjusting of this special glass (or plastic) this electric action can be transmitted and transposedwithout disturbance of the image it carries-in a plane differently oriented and of much greater linear dimensions than the initial vision or scanning plane.

A black filter of great linear dimensions conveniently adjusted to this greater glass or plastic surface carrying these electric impulses, can be operated from a much smaller television scanning screen, or much smaller vision camera. The projection of strong light through this black filter will reproduce with great brightness and in greatly enlarged size the small initial electronic image.

Fig. 30 shows schematically an image intensification camera provided with the screen 8| protecting the photocathode l2 from lateral light projection. This screen is constituted from a relatively thick glass plate with linear electric conductivity, but of completely opaque, non-transparent glass, which will be called black glass. Between this black glass screen 8| and the black filter 83, of one of the above described types (for instance of Fig. 29), is interposed a thick glass plate 82 with linear conductivity, but nearly completely transparent.

The plates 8|, 82 and the black filter 83 are closely applied together in such a manner that the ducts or strands 18 of the respective plates are electrically connected-duct per duct-so as to form a multitude of continuous ducts transmitting the electric charges, point by point, to the black filter. These individual electrical connections between the ducts of two such surfaces can, for instance, be insured by covering one of the surfaces with a regular mosaic of small mutually insulated metallic areas, each area being in electric contact with the corresponding duct. On the opposite contact surface the ends of the ducts may be thickened by electrolytic deposit of an excess of any ductible metal, so that the electric contact between the mosaic elements and the ends of the ducts will be insured by simple pressure between the surfaces. The surfaces can be, if necessary, stuck together by an appropriate insulating paste, or both surfaces can have accurately coordinated mosaics, and an insulating paste with fine suspension of a ductile metal can be applied between the surfaces; after squeezing the paste the suspended particles will insure the contact. In cases when the black filter surface is shaped in form of light concentrating convexities (as shown in Figs. 28 and 29), the remaining space between these convexities and the plane surface of the plate 82 can be filled if desired with a material of low refraction index, or glasses with different refraction index may be used, the matching surfaces being shaped with complementary concavities and convexities fi-t ing together and insuring the light concentration.

Preferably the black plate 8| (Fig. 30.) will be welded to the walls of the vacuum camera which contains the photocathode l2, and which can, if desired, contain the secondary electron amplifying device (such as 25, Fig. 10 or 41, Fig. '17). The electron receiving surface of the black plate 8|, has a mosaic of metallic areas coordinated with respective ducts or strands.

If desired the plate 82, assumed tobe rectangue lar, can be cut into three prisms as shown by dotted lines 84, with non-transparent reflecting surfaces, reflecting the laterally projected light (shown by arrows) on the black filter.

Fig. 31 shows the transmission of' electronic action of the vision camera containing the photocathode |2 and the black wall 8|, to the black filter 83, through a transparent body 85, with conductive strands going in oblique direction from the black wall to the black filter, the light being projected on the black filter directly by the source 86 and the lens 81, from the same direction from which comes the image. The light valves are assumed to be the type with liquid suspension, so that a positive image is reproduced at the exit of the black filter.

Fig. 32 shows a similar arrangement comprising; the first photocathode l2, the black plate 8|, ducts 18 going to the first black filter 83 "with sensible salt; a light from the source 86 projected through the black filter 83 on the second photocathode I2 a second black plate 8| the ducts I8 going to the second black filter 83 supposed to be also with sensible salt; and light from the source 86 projecting through this filter a positive image. In this figure the ducts are curved (but they could also be straight.

Fig. 33 shows a black filter with sensible salt placed at the end of a transparent glass block with linear conductivity, the filter being maintained at high temperature by inductive electric heating by the ring 88 and being protected from excessive heat losses by a transparent Dewar capsule 89. The other end of the glass block is conveniently applied to a wall with linear conductivity of a television or vision tube, which can remain at relatively low temperature.

, Figs. 34 and 35 show an example where the electric action of a scanning television beam (or of an electronic image projected in a vision camera) is transmitted to a screen, such as a television or vision screen with much larger dimensions than the initial electronic image.

In Fig. 34, the wall of glass 90 with linear conductivity forms the scanning screen of the television tube; an optional intermediate block 9| with linear conductivity is applied and conveniently adjusted to the wall 98; 98 is a body with linear conductivity, preferably of a convenient plastic which need not be transparent, composed of a multitude of sheets or laminae M 98 is a large square plate with linear conductivity, of a transparent plastic material. The vertical plastic laminae composing the plate 90 are oriented perpendicularly to the large surface of the plate and at right angles to the laminae 9| composing the body 98 The laminae 9| of the plate 88 contain divergent conductive strands or ducts H3 connecting the ducts 18' of the body 98' with the ducts 18 of the body 90 which run tov the large surface of the plate 98 to which a black filter 83 of large dimensions is conveniently applied. This black filter may, if desired, be formed of a certain number of small black filters. The ducts 18 need not form straight lines, but can for instance form curves which come out normally to the surface. A suitable number of pro.- jection lamps 92 project light through the black filter and reproduce the television, or vision image.

Fig. 35 is a section on the median plane of Fig. 34. In this figure I0 are the divergent conductive ducts connecting the ducts 18" with the wider spaced ducts 18 of the plate 90 93 are theexit points of the ducts m which cover the surface of the plate with a multitude of conductive points at regular intervals from each "other.

Fig. 36 shows in perspective a normal block of plastic material or glass with linear conductivity, from which other forms can be cut or can be derived. l'n this figure 94 are the laminae; 95, the exit points of theducts at. The dotted line 91 shows a possible cut in the block inorder to provide a plate or wall with linear conductivity.

Fig. 37 shows the case when the scanning receiving wall of a television tube is constituted by a thin glass lamina 93 with linear conductivity, mechanically consolidated with a thick plastic plate 9.9 with linear conductivity, strongly stuck to the glass plate. The thin glass plate 93 attached to the television tube can, if desired, be formed by a multitude of fine perforations made for instance by electric sparks or any other method, and filled with metal by electrolytic deposit, or other procedures.

Conductive strands or ducts can be made for instance by covering a glass or plastic lamina with a fine protecting layer ofappropriate maskmaterial, and then by removing this material along a multitude of fine lines, as by suitable mechanical devices. The metallic deposit can then be made along these exposed lines by any known procedure, for instance vacuum deposit, or silvering etc., with reinforcement by electrolytic deposit if necessary. Or else, narrow grooves can be made on glass laminae, filled with metallic or conductive deposit or material, or a conductive paste containing metal or carbon, and the surface then being cleaned.

The glass laminae are welded together when absolute tightness is needed, or they can be secured by a suitable adhesive. Plastic laminae are Welded or stuck by any appropriate means. It is provided that by use of deposits of special metals or conductive agglomerations the bodies of linear conductivity can be deformed, stretched, changed in section etc., without destroying the continuity of the conductive ducts.

The number of strands or ducts corresponds at least to the number of points constituting the television or vision image. For instance the scanning wa of a television tube with 200,000 points of an image of 18 cm. of linear dimension Will have 260,009 ducts at a mean distance from each other of M mm.

The same number of vision screen of 2.2 mm.

For the body with linear conductivity shown in Figs. 3a and 35 and consisting in at least two blocks with difierently oriented initial laminae in each, can be substituted a single block or plate constituted of a multiplicity of thin sheets, for instance of plastic material, parallel to the surface of the final large screen, each sheet having part with ducts or strands, these ducts continuing, on the large square part of the plate, in more distant parallel ducts. This part of the plate with parallel ducts can be then out, oblique to the great surface, forming thus a stretched prismatic body, the ducts terminating on the cut surface at equidistant points, ready for connection with a large black filter. The unified body may consist in a multitude of plastic laminae perpendicular to the surface of the great screen, these laminae being of variable thickness (similar to those shown in Fig. 35 but without interruption). The ducts are conveniently shaped and ducts on the final telel m? will have a means distance 26 terminate at the great screen surface at equidistant points.

The invention provides that the metallic ducts in the body with linear conductivity can be constituted not only by fine metallic deposits but also by fine wire strands of appropriate metal or alloys such as silver, copper, tungsten, platinum, etc., fixed on the surface of the laminae before their putting or welding together.

The incorporation of the ducts in the plastic material can be made by fixing the metallic Wire on a rotating cylindrical surface covered with plastic and by depositing then a layer of plastic material in a state of solidification or already solidified, increasing the thickness of the rotating body by alternating layer and wires superposition. The distance between the wires and their angular orientation can be controlled and periodically changed, if necessary, by appropriate devices.

What I claim is:

1. Apparatus forintensifying electronic images comprising, a-source of electrons, a black filter of opaque material having a multiplicity of electr-onwonductive orifices distributed throughout the area of the filter", the total cross-sectional area of said orifices being a small fraction of the total filter area, electron-responsive material associated with said orifices and adapted to constitute light valves controlling the passage of light through andbeyond said orifices, and means for concentrating the electrons of a unit crosssectional area substantially greater than the area of each orifice on the electron-responsive material associated with the orifice included within said unit area.

2. Apparatus according to claim 1 which includes a relatively extended electron-receiving area adjacent each orifice, and means for concentrating the electrons received by said area in the most restricted part of the orifice.

3. Apparatus according to claim 1 which includes a relatively extended crystalline salt area adjacent each orifice in continuity with a body of crystalline salt in the most restricted part of the orifice.

4. Apparatus according to claim 1 which ineludes a relatively extended transparent metallic area adjacent each orifice in electrical communication with a body of crystalline salt in the most restricted part of the orifice.

5. Apparatus according to claim 1 which includes a high frequency vibrating quartz plate adapted to vibrate the electron-responsive material.

6. In an apparatus for intensifying electronic images, a black filter comprising a body of opaque material traversed by a multiplicity of small orifices distributed throughout the area of the filter, and optical means associated with said orifices for concentratmg light projected on Said filter in said orifices.

7. An apparatus according to claim 6 in which the optical means comprise suitably shaped crystalline salt bodies extending into the orifices.

8. An apparatus according to claim 6 in which the optical means comprise inverted cone shaped crystalline salt bodies having their apexes extending into the orifices.

9. An apparatus according to claim 6 in which the optical means comprise suitably shaped bodies of transparent material having transparent electron-conductive material on their surfaces and extending into contact with a conductive material in the orifices.

10. In an apparatus for intensifying electronic images, a black filter comprising a body of opaque material traversed by a multiplicity of small orifices distributed throughout the area of the filter, and optical means associated with said orifices for directing in a parallel beam the light emerging from said orifices.

11. In an apparatus for intensifying electronic images, a black filter comprising a body of opaque material traversed by a multiplicity of small orifices distributed throughout the area of the filter, means for scanningthe filter with an electronic television scanning beam, a source of light projected on the filter, optical means associated with said orifices for concentrating said projected light in the orifices, and optical means associated with said orifices for directing in'a parallel beam the light emerging 'from the orifices.

12. Apparatus according to claim 11 which includes, electronically actuated light valves adapted to control the passage of light through and beyond the orifices, and means for concentrating the electrons of the scanning beam in each orifice for actuation of the respective light valve.

13. The method of intensifying electronic images formed in a screen including electronresponsive material adapted to vary in transparency as a function of electronic action which comprises, directing a'stre'am of electrons toward said screen and concentrating the electrons of a unit cross-sectional area on a section of said electron-responsive material the area of which is a small fraction of said unit area.

14. The method according to claim 13 which includes projecting a beam of light through and beyond said section of material under the control of said concentrated electrons.

15. The method according to claim 14 which includes concentrating a unit cross-sectional area of said light beam on the corresponding section of material.

16.The method according to claim 14 which includes preventingthe passage of light through and beyond any areas of the screen other than those on which the electrons are concentrated.

17. The methodaccording to claim 13 in which the stream of electrons is a scanning beam.

CONSTANTIN CHILOWSKY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re. 22,115 Herbst June 16, 1942 2,121,990 Schroderet a1. June28, 1938 2.277008 Von Ardenne Mar. 17, 1942 2277,009 Von Ardenne Mar. 17, 1942 2335659 Fraenckel et 8.1. Nov. 30, 1943 2,366,319 Donal, Jr Jan. 2, 1945 

